1. Field of the Invention
The present invention relates to a communication apparatus which can selectively execute speech communication and data communication.
2. Related Background Art
As an apparatus of this type, a facsimile device which communicates image data has been known. Prior art facsimile devices have a function to automatically determine whether a calling station is a human (telephone set) or a facsimile device when it receives a call (hereinafter TEL/FAX automatic switching function). There have been known three methods for implementing the TEL/FAX automatic switching.
In a first method, after a line has been captured at the reception of a call, a voice message (for example, "please say hellow if it is a telephone and depress a start button if it is a facsimile device") is sent to a calling station, and a signal from the calling station is thereafter monitored. If voice is detected, it is determined that the calling station wants the speech communication and a bell in the facsimile device or a built-in telephone set is rung to call an operator. If the signal from the calling station is a CNG signal (call tone signal) or if the no signal status continues for longer than a predetermined time period (t.sub.2), it is determined that the calling station is a facsimile device, and a called device identification signal (CED) and a digital identification signal (DIS) are sent out and the facsimile communication is then automatically started. (See FIG. 8A).
In a second method, after the line has been captured at the reception of the call, no response is made for a predetermined time period (t.sub.3) and the CNG signal or voice signal from the calling station is monitored. Like in the first method mentioned above, if the voice signal is detected, the operator is called, and if the CNG signal is detected or no signal is detected during the time period t.sub.3, the facsimile communication is automatically started. (See FIG. 8B).
In a third method, when a call is received, an operator is called without capturing the line for a predetermined time period t.sub.4 (which may be arbitrarily set). If an off-hook state of a hand set by the operator is detected during the time period t.sub.4, the device subsequently functions as a telephone set, and if no off-hook state is detected in the time period t.sub.4, it is determined that the calling station is a facsimile device and the facsimile communication is thereafter started. (See FIG. 8C).
The techniques of the TEL/FAX automatic switching described above are disclosed in U.S. Pat. No. 4,677,660, U.S. Pat. No. 4,663,778, U.S. Pat. No. 4,815,121, U.S. Pat. No. 4,800,439, U.S. Pat. No. 4,932,048, U.S. Pat. No. 4,916,607 and U.S. Pat. No. 4,353,097.
The prior art devices, however, include the following problems.
In the first method, the voice response is hard to listen if a line condition is bad.
Further, if a person at the calling station is not accustomed to the voice response, it may happen that the absence of operator at the called station is determined at a stage of the first voice message and the line is opened. Further, it is unnatural to force the person at the calling station to speak.
Further, as shown in FIG. 8A, 10-15 seconds are required for t.sub.1, 5-10 seconds are required for t.sub.2, and total of 15-25 seconds are required. As a result, a considerable time is required for the TEL/FAX automatic switching.
In the second method, since no voice response is given to the calling station for t.sub.3 (5-10 seconds) time period, it imparts a strange feeling to the operator, who may consider that there is trouble on the line and may open the line.
In the third method, if the calling station is a facsimile device, the t.sub.4 time period is always required before the facsimile communication is started, and smooth switching to the facsimile communication is not attained.
Further, if the operator at the called station does place the line in a hook off state in t.sub.4 time period, the facsimile communication is started even if the calling station is a telephone set. Accordingly, an efficiency of the TEL/FAX switching is low.